Trouble with face me objects in V-Ray...

[joostmee]

In sketchup i have face me objects (trees) with shadows set to face the sun. This shows up correctly.

When I render the scene in V-Ray, the sun cuts across the face me object not perpendicular to the sun, producing incorrect "thin" shadows.

Does anyone know what to do about this?

Also the faceme object in sketchup view does not display the alpha, so the trees have a black area around them, when rendered the alpha works great.

I am using a trial version of V-Ray 7 with sketchup 7 PRo.

[dalomar_cg]

Re: Trouble with face me objects in V-Ray...

As to the alpha in the viewport, SU only "understands" the integrated alphas loaded from PNGs and TIFFs, so it doesn't get the separate alpha that we use for rendering.

As to why the face me objects aren't acting correctly, I'll have to look into this a little bit more. Someone with a little more SU knowledge than me might be able to shed some light on this though.

[remon_v]

Re: Trouble with face me objects in V-Ray...

I have the same problem.... even tho I turn the "cast shadows" off

[Jackson_cg]

Re: Trouble with face me objects in V-Ray...

The face-me components are acting exactly as they're supposed to, as is VRay. The shadows for your clipmapped trees only render as thin shadows because VRay can only see the geometry (i.e. a flat face, side-on towards the VRay sun) and the clipmapped diffuse texture (as Dalomar said). The "shadows to face sun" and "cast shadows" are features of SU, not VRay hence they display "correctly" in SU, but not VRay.

EDIT: I'm working on a workaround now.

[dalomar_cg]

Re: Trouble with face me objects in V-Ray...

In the future (ie in the next full version of VfSU), you should be able to get around rendering twice by having two trees in the file. One that renders as normal facing the camera, and another that faces the shadows that is invisible to the camera....the benefits of per object properties.

[Jackson_cg]

Re: Trouble with face me objects in V-Ray...

Sounds great, but unfortunately that particular feature won't solve this problem as the invisible tree faces will still cast a shadow onto the visible tree faces, so one vertical half of the tree will been in stark shadow while the other is brightly lit... with a very straight boundary between the two. The key (on top of implementing the feature you described) is to ensure the invisible faces cast shadows on everything but the visible tree faces. I've had a mess around with this problem before and now that I experiment again I realise what a head-scratcher it is.

The reason I haven't done too much digging around with this before is because clipmapped billboard trees generally look like cr*p when the sun is at an acute angle to them anyway. They really need to have the sun at less than 45° from their normal direction to look good and if that's the case then the shadows cast well enough that it's not really an issue.

[dalomar_cg]

Re: Trouble with face me objects in V-Ray...

There should be a way to set the face me tree to be either invisible to direct light, set it so it won't generate shadows, or set the shadow tree not to receive shadows. I'll check up on whether those are available or not.

[jrharvey]

Re: Trouble with face me objects in V-Ray...

In the future (ie in the next full version of VfSU), you should be able to get around rendering twice by having two trees in the file. One that renders as normal facing the camera, and another that faces the shadows that is invisible to the camera....the benefits of per object properties.

I dont use sketchup but that is soooo cool. I wish you could do that for rhino.

[dalomar_cg]

Re: Trouble with face me objects in V-Ray...

yep it will be there. At this point, with all the changes that have been done to the core, Rhino and SketchUp are more linked than ever, so there's very little (if any) additional work required for getting it available for one platform as opposed to another. Of course this doesn't include issue that are platform specific (ie RDK stuff in Rhino, or light types in SU)

[Jackson_cg]

Re: Trouble with face me objects in V-Ray...

I've worked out a workaround.

In each billboard tree component you have to create an identical face rotated at 120° so that when the whole face-me tree component is facing you, you can only see the back face of the rotated face. As we want this face to be invisible (but still cast a shadow) we paint the back of it with a 100% transparent material (obviously without reflection or refraction).

The trouble is, this would still cast shadow onto the visible face-me tree face, so we have to rotate it horizontally (i.e. down towards the ground plane about it's bottom edge axis) until it no longer intersects the face-me tree face. This way it only cast shadows on objects other than itself. This will work best with tall thin trees and if trees are not too close to buildings as the "fake shadows" face can interfere with their geometry, meaning that rather than casting a shadow onto them as a tall tree would in real life, the fake-shadow face will actually intersect the building.

[Jackson_cg]

Re: Trouble with face me objects in V-Ray...

The tree I've used below is just about the worst type to use this method for- very wide and with a very low canopy, so it runs into all the problems described above of the fake shadow face intersecting buildings, but nevertheless it achieves a pretty good shadow result from a billboard tree and with only two materials per tree- one diffuse and one 100% transparent (of course the transparent material can be used once for all trees in a model). Of course if we could turn off shadows for the diffuse face the result would be even better, without the extra, thin shadow cast on the ground in the direction of the VRay sun. In my case I actually modelled the trunk very roughly so it intersects the ground properly and pulled the foliage face foward so it casts a shadow on the trunk, but the attached SU views just show a simple two- face, face-me component.



I've shown a bird's eye view of the actual SU tree component, which shows the diffuse face outlined in blue and the "invisible" shadow-casting face outlined in red for clarity. Likewise for the second worm's eye view, which shows the visible side of the shadow-casting face.

[remon_v]

Re: Trouble with face me objects in V-Ray...

sounds great could u send me skp file so I can have look and understand it better? remonvergeer@hotmail.com